1. Field of the Invention
The present invention relates to a system and method for bone fracture fixation.
2. Description of the Prior Art
Conventional bone fracture fixation plate and screw systems work by drawing the fracture fragments to the plate, and if designed with “compression” holes, the fracture fragments can be made to compress against each other to promote primary bone healing. However, the angular relationship between the plate and screws is not fixed and can change postoperatively. As such, this can lead to misalignment and poor clinical results.
One method of securing the screw to a bone plate involves the use of so-called “locking screws.” A locking screw has a male thread on an outer surface of its head that interfaces with a female thread on the plate to lock the screw to the plate. Bone plates having threaded holes for accommodating locking screws are known. For example, German Patent Application No. 43 43 117 discloses a bone plate with threaded holes for locking screws. As the relationship between the locking screws and the plate is fixed, locking screws provide a high resistance to shear or torsion forces. However, locking screws have a limited capability to compress bone fragments.
Another approach to construction of a bone plate involves use of “combination holes.” Combination holes in the bone plates have a domain for non-locking screws and another domain for locking screws. The locking screws can only be applied in a direction perpendicular to the plate. (See, e.g., U.S. Pat. Nos. 6,669,701 and 7,354,441 to Frigg) However, only a one locking or a non-locking screw can be applied in each of these “combination” holes along the bone plates.
Another bone plate hole configuration involves a “figure-eight” hole. (See, e.g., Universal Locking System available from Zimmer Holdings, Inc. (Warsaw, Ind.); see, also J. Bone and Joint Surgery, 89(7) 2007.) The figure-eight hole in the a bone plate has two parallel threaded domains. A locking screw can be mated to one domain of the holes or to the other domain of the same hole. In either case, the locking screw can be applied only perpendicular to the bone plate. Further, only one screw can be applied in each of these “figure-eight” holes along the plate.
In yet another approach, the bone plate has individual locking holes for mating individual locking screws. (See, e.g., MIS Technique available from Zimmer Holdings, Inc. (Warsaw, Ind.)) The individual holes are oriented alternating in one direction and in another direction (in the plane transverse to the longitudinal axis of the plate) away from the perpendicular to the plate. However, for such a configuration, half of the screw holes may not be suitable for use. In the worse case scenario, none of the holes can be used.